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The species-mixed Pilosella populations comprising diploid sexual and polyploid facultatively apomictic biotypes were studied in Bulgaria. Parentage of co-occurring recent hybrids was inferred from a combination of morphology and ploidy level that corresponded to simple/multiple crosses of basic species via either reduced or unreduced gametes. The flow cytometric seed screening illustrated the capacity for heteroploid hybridization both in open-pollinated plants in the mixed-ploidy populations and in crossing experiments. The diploid sexual species in Bulgaria have a limited impact on interspecific hybridization, and simple inter-cytotype hybrids are only sporadically formed. The origin of the most common hybrids in Bulgaria that are apomictic and retain the pentaploid/hexaploid ploidy level of a co-occurring putative apomictic parent remains unclear. The absence of stabilized hybridogeneous species and scarcity of commonly hybridizing polyploid sexual biotypes are crucial attributes that distinguish the Pilosella populations in Bulgaria from those in the Czech Republic and Germany. No recent high-polyploid hybrids of 2n + n origin that would potentially become drivers of ongoing hybridization in the mixed sexual-apomictic Pilosella populations similar to those in Central Europe have been recorded in Bulgaria. The pattern of co-occurring cytotypes in Bulgaria likely limits interspecific hybridization due to stronger ploidy barriers. Citation: Krahulcová A., Krahulec F. & Vladimirov V. 2018: Impact of interspecific hybridization within a polyploid agamic complex of Pilosella (Asteraceae, Cichorieae) in Bulgaria compared with Central Europe. – Willdenowia 48: 345–362. doi: https://doi.org/10.3372/wi.48.48302 Version of record first published online on 8 October 2018 ahead of inclusion in December 2018 issue. [ABSTRACT FROM AUTHOR]

We studied the significance of sexual reproduction as a source of ploidy level variation in a model system consisting of hexaploid, facultatively apomictic Pilosella bauhini and tetraploid, sexual P. officinarum. As the maternal parent, apomictic P. bauhini generated higher ploidy level variation than sexual P. officinarum. Ploidy levels of its progeny ranged from triploid to octoploid under experimental conditions and even to decaploid in the field. This progeny diversity resulted from the breeding system in P. bauhini, which included haploid parthenogenesis and sexual reproduction through both reduced and unreduced gametes besides prevailing apomixis; these particular reproductive pathways have been quantified. Sexual P. officinarum, on the other hand, reproduced exclusively through fusion of reduced gametes and produced only pentaploid hybrids or tetraploid progeny from autogamy, allogamy or both. Surprisingly, sexual P. officinarum was also the species showing stronger reproductive isolation, especially under the field conditions where intra-specific fertilization was highly favoured, most probably through competition between conspecific and heterospecific pollen. Apomictic P. bauhini thus appeared to be a significant source of ploidy level variation in the model population even though most of its progeny was formed clonally through apomixis. Only part of this variation was manifested in the field. [ABSTRACT FROM AUTHOR]

The capacity to generate variation in ploidy and reproductive mode was compared in facultatively apomictic versus sexual maternal plants that coexist in two model populations. The population structure was studied in polyploid hybrid swarms comprised of Hieracium pilosella (usually sexual, less commonly apomictic), H. bauhini (apomictic), and their hybrids (sexual, apomictic, or sterile). Relationships among established biotypes were proposed on the basis of their DNA ploidy level/chromosome number, reproductive mode and morphology. Isozyme phenotypes and chloroplast DNA haplotypes were assayed in the population that was richer in hybrids. The reproductive origin of seed progeny was identified in both sexual and apomictic mothers, using alternative methods: the karyological, morphological and reproductive characters of the cultivated progeny were compared with those of respective mothers, or flow cytometric seed screening was used. In both populations, the progeny of sexual mothers mainly retained a rather narrow range of ploidy level/chromosome number, while the progeny of facultatively apomictic mothers was more variable. The high-polyploid hybrids, which had arisen from the fertilization of unreduced egg cells of apomicts, mainly produced aberrant non-maternal progeny (either sexually and/or via haploid parthenogenesis). Apparently, such versatile reproduction resulted in genomic instability of the recently formed high-polyploid hybrids. While the progeny produced by both true apomictic and sexual mothers mostly maintained the maternal reproductive mode, the progeny of those ‘versatile’ mothers was mainly sexual. Herein, we argue that polyploid facultative apomicts can considerably increase population diversity. [ABSTRACT FROM AUTHOR]